1. Field of the Invention
The present invention relates to a ship incorporating a pod propulsion unit in addition to a main propeller, and an operating method therefor.
2. Background Art
Recently, in propulsion devices for ships, in the case where the thrust generated by the main propeller is insufficient, it has been suggested, in order to increase the thrust, to provide a pod propulsion unit to the rear or the front of the main propeller at a position which does not interfere.
FIG. 9 shows related technology explained in Japanese Patent Application No. 2001-199418, which was filed by the assignee of the present application on Jun. 29, 2001 and has not been published yet. In the technology shown in FIG. 9, reference symbol 1 denotes the stern of the hull of a ship, 2 denotes a main propeller for generating the main propulsive force for propelling the ship, while 10 denotes a pod propulsion unit. The main propeller 2 is rotated by a driving force from a drive mechanism (omitted from the figure) such as a diesel engine (generally referred to as the main engine).
The pod propulsion unit 10 is furnished with a casing 11, a pod propeller 12, a strut 13, and a support 14.
With regards to the casing 11, the pod propeller 12 is provided at an approximately circular cylindrical rear portion or front portion, or at both the front and rear portions (not shown in the figure). The pod propeller 12 has the function of generating a propulsion force by rotation thereof. An electric motor for driving the pod propeller 12 is provided inside the casing 11.
The strut 13, of air foil section, is provided on the upper portion of the casing 11. The support 14, which constitutes the overall turning axis for the pod propulsion unit 10, is provided on the upper end of the strut 13. The support 14 is connected to a drive mechanism (not shown in the figure) provided on the hull side. Hence the pod propulsion unit 10 is provided so that the whole unit can be turned with respect to the stern 1 of the ship via the support 14.
The ship constructed in this way obtains a propulsive force by rotating the main propeller 2, rotating the pod propeller 12, or rotating both the main propeller 2 and the pod propeller 12 together. Furthermore, by turning the pod propulsion unit 10 about the support 14, the strut 13 demonstrates a steering function to give a steering force, and thus turn the ship.
In the above described ship, high speed cruising, faster than for a ship equipped with only the main propeller 2, is possible. Furthermore, the strut 13 of the pod propulsion unit 10 can be used as a rudder. Consequently, when steering, particularly at the time of high speed cruising (for example, cruising in excess of around 20 knots), an excessive hydrodynamic force acts on the strut 13, so that a very large force is applied to the support 14. Therefore, there is a problem in that the support mechanism for supporting the support 14 and the turning mechanism for turning the pod propulsion unit 10 must have sufficient strength, that is, these must involve large mechanisms.
The present invention takes into consideration the abovementioned circumstances, with the object of providing a ship and an operating method therefor so that the support mechanism and the turning mechanism and the like of the pod propulsion unit, arranged at the rear of the main propeller, can be simplified and cost can be reduced.